Anticancer therapies designed to counter cancer-specific pathways have a substantial impact on patient survival in several cancers. However, even among those patients that show initial response to currently available anticancer therapy, drug-resistant clones frequently evolve by a variety of mechanisms. Ultimately, resistance to chemotherapy results in treatment failure, which is the main reason why cancer remains a deadly disease. Multidrug resistant (MDR) cancer cells are able to resist multiple cytotoxic agents with distinct targets. One of the best characterized mechanisms of multidrug resistance is the increased drug efflux mediated by ATP-binding cassette (ABC) transporters, in particular P-glycoprotein (P-gp, MDR1, ABCB1) (Gottesman et al. 2002) (Szakacs et al. 2006). ABC proteins, present in all living organisms from prokaryotes to mammals, are transmembrane proteins that control the passage of their substrates across membrane barriers. ABC transporters make up a complex cellular defense system responsible for the recognition and the energy-dependent removal of environmental toxic agents entering the cells or organisms (Sarkadi et al. 2006). In cancer, P-glycoprotein acts as a primary shield that keeps intracellular chemotherapy drug levels below a cell-killing threshold. Cancer cells overexpressing P-glycoprotein become multidrug resistant, as the promiscuity of P-glycoprotein (P-gp) allows the efflux of most clinically used anticancer agents (Türk & Szakács 2009). The contribution of P-gp to poor chemotherapy response was convincingly demonstrated in hematological malignancies, sarcomas, breast cancer, and other solid cancers (Szakacs et al. 2006). Recently, acquired doxorubicin resistance was associated with increased expression of the mouse Mdr1 genes in a genetically engineered mouse model for BRCA1-related breast cancer. Significantly, even moderate increases of Mdr1 expression were found to be sufficient to cause doxorubicin resistance, which could be reversed by the third-generation P-gp inhibitor tariquidar (Pajic et al. 2009). These results confirm that P-gp indeed plays a pivotal role in causing drug resistance in a realistic model of cancer.
Unfortunately, clinical studies conducted with several generations of P-gp inhibitors have failed and the pharmaceutical industry seems to have abandoned the concept of P-gp inhibition (Libby & Hromas 2010).
However, there is still a need for compounds which act as efficient cytostatic and/or chemotherapeutic agents against multidrug-resistant cancer cells with minimal side-effects, as well as for compounds which are suitable for decreasing or eliminating multidrug resistance in cancer cells, thus making them sensitive to existing chemotherapeutic agents.
It was suggested that an alternative strategy to overcome MDR may rely on the concept of collateral sensitivity, first introduced to describe the paradoxical hypersensitivity of drug resistant bacteria against certain compounds (Szybalski & Bryson 1952). According to this concept the objective to treat multidrug resistant cancer could be fulfilled by providing compounds exhibiting selective and preferential cytotoxicity against multidrug-resistant cell lines. Thus, these cell lines, while resistant to one or more drugs, pay the fitness cost of resistance by becoming sensitive to other drugs. Multidrug resistant cells overexpressing resistance-providing transporters exhibit collateral sensitivity against MDR-selective compounds that are selectively toxic to the transporter-expressing cells.
A review of the scientific literature identifies several compounds that were reported to be preferentially toxic against P-gp-expressing cells (Szakács et al. 2014). Most compounds were identified in studies that were undertaken with the intent of characterizing the extent of drug resistance in multidrug-resistant cells.
In several cases (e.g. tiopronin (Goldsborough et al. 2011)), however, the test compounds' MDR-selective activity was found to be restricted to a specific MDR cell line. In such cases, selective toxicity toward P-gp-expressing cells could not be reversed by inhibition of P-glycoprotein, and P-gp-transfected cells and a number of other resistant P-gp-expressing cells were not hypersensitive to the compounds. These data suggested that a molecular alteration in multidrug-resistant cells, not related to P-gp expression, was responsible for the hypersensitivity of cells to such compounds. Thus, in these cases P-gp expression was either not necessary or not sufficient to make the MDR cell hypersensitive against the drugs tested.
Different studies report outstanding MDR-selectivity of desmosdumotin derivatives (Nakagawa-Goto et al., 2010) and Dp44mT (Jansson et al. 2015), which findings, however, were not found to be reproducible in further MDR cell lines expressing P-gp.
In contrast, in the specific case of collateral sensitivity, the toxicity of certain MDR-selective compounds is uniformly increased by the P-gp transporter protein in P-gp-expressing MDR cells e.g. in comparison with control cells not expressing P-gp, whereas this toxicity is abrogated in the presence of P-gp inhibitors (Szakács, Annereau, Lababidi, Shankavaram, Arciello, Kimberly J. Bussey, et al. 2004; Türk et al. 2009). This reveals that in addition to the export of toxic substrates, P-gp can directly sensitize MDR cells against these P-gp-potentiated MDR-selective compounds (Szakács et al. 2004; Ludwig et al. 2006; Türk et al. 2009; Hall et al. 2009). Ludwig et al. describe that cells become hypersensitive to NSC73306 in proportion to their P-gp function, and this selectivity is abrogated by functional inhibition or downregulation of P-gp, thereby supporting the causal link between toxicity and P-gp function (Ludwig et al. 2006).
As it comes from the above analysis, according to this approach MDR-selective compounds applied for treating of MDR cancer can selectively destroy cells expressing the transporter responsible for drug efflux-based multidrug resistance (i.e. P-gp).
Several classes of compounds having MDR-selective activity have been disclosed in the state of the art.
The published International Patent Application WO2006009765 discloses diverse compounds capable for reversing multidrug-resistance in cancer cells. The application relates to a method of inhibiting the growth of neoplastic cells by administering to the subject an antiproliferative agent, wherein the antiproliferative effect of the agent is potentiated by P-gp (i.e. the ABCB1 transporter), including the case when said neoplastic cells have already been exposed to an anti-cancer therapeutical agent which is substrate to P-gp. The application furthermore relates to a method for inhibiting the development of multidrug resistance.
International Patent Applications WO2009102433 and WO2012033601 disclose thiosemicarbazone derivatives having MDR-inverse (i.e. MDR-selective) activity which are effective against multidrug-resistant cells. The selective cytotoxicity (“MDR1 selectivity”, see Table 1) has been assessed as a ratio of the “absolute” cytotoxicity of the disclosed compounds measured using the MTT assay in the parental P-gp-negative adenocarcinoma cells to the cytotoxicity determined in an adenocarcinoma cell line expressing high levels of P-gp. The concept of determining the ratio of cytotoxicity of a parental, non multidrug-resistant cell line to the cytotoxicity of a multidrug-resistant cell line is referred to in this specification as determining selective toxicity ratio, selectivity ratio (SR) or briefly, selectivity. Selectivity of the compounds disclosed in WO2009102433 and WO2012033601 are generally lower than approx. 9 and 14, respectively.
International Patent Application WO2012058269 discloses compounds belonging to the class of tiopronins capable of reversing multidrug resistance, exhibiting selectivity up to 51.0. However, tiopronins can not be regarded as MDR-selective compounds in the sense MDR-selectivity is used in the present invention since these do not confirm the criteria thereto described above.
International Patent Application WO2014078898 discloses metal, especially iron and copper complexes of substituted hydrazons, semicarbazones and analogues thereof without disclosing their selectivity.
In the paper of Orina et al. (Orina et al. 2009), correlations were assumed between the expression profile of 48 human ABC transporters and the growth inhibitory profiles of candidate anticancer drugs in the NCI60 cell panel. Orina et al. disclose in the above-mentioned paper that the compound NSC693871 [7-(pyrrolidin-1-ylmethyl)quinolin-8-ol hydrochloride] exhibits selectivity in the order of magnitude of 10 in respect of ABCB1-overexpressing and parental HEK293 cells.
International Patent Application WO2010138686 and Türk et al. (Dóra Türk, Matthew D. Hall, Benjamin F. Chu, Joseph A. Ludwig et al., 2009) discloses compounds suitable for eliciting the reversal of multidrug-resistance. These publications disclose that the 8-hydroxy-quinoline derivatives NSC693871 (see above) and NSC693872 [7-(N,N-diethylaminomethyl)quinolin-8-ol] exhibited selectivity of about 8.48 and 3.90, respectively.
International Patent Application WO2011148208 discloses substituted 8-hydroxyquinolines which are useful for the treatment of diseases associated with neurological and/or oxidative stress. This reference indicates the cytotoxic effect of some compounds in cancer cell lines but is silent with respect to their selectivity and potency.
A further patent search revealed several documents which disclose compounds falling within the scope of the general formula (I) of the claims discussed below. However, some of these documents do not mention any pharmacological effect (i.e. they concentrate on the synthesis way) while the remaining documents declare a very different pharmaceutical utility for the disclosed compounds. Here we list these documents and give in brackets the relevant parts thereof, mentioning the effect, too, if any.    J. Med. Chem., 56(2), 521-533 (2013) (Compound 13; having Catheprim B inhibitory activity);    Acta Pharmaceutica Jugoslavica, 33(3-4), 199-208 (1983) (Compounds 5, 7 and 11, having antibacterial activity);    FR 2160718 A1 (Roussel) (1973 Jul. 6) (Example 1, having antibacterial activity);    ChemMedChem, 11(12), 1284-1295 (2016 Feb. 16) (Compounds 6a and 6b, having anti-Alzheimer activity);    WO 2010/042163 A2 (Johns Hopkins Univ.) (2010 Apr. 15) (Compound 2b), having angiogenesis inhibitory activity);    WO 96/09291 A1 (Henkel) (1996 Mar. 28) (Example 1—no activity is disclosed);    U.S. Pat. No. 2,681,910 (Burckhalter) (1954 Jun. 22) (Example 10—no activity is disclosed);    Trudove na Nauchnoizsledovatelskiya Khimikofarmatsevtichen Institut, 15, 71-80 (1985) & Caplus abstract (AN:1986:552901)—no activity is disclosed    J. Virology, 84(7), 3408-3412 (2010) (FIG. 3, having anti-prion activity);    Heterocycles, 68(3), 531-537 (2006) (Compound 3—no activity is disclosed);    Biomedical Chromatography, 28(1), 142-151 (2014) (Compound 12 to 15—no activity is disclosed);    J. Org. Chem., 26, 4078-4083 (1961) (Compounds (I) and (IV)—no activity is disclosed).
These compounds are excluded from the scope of claims by disclaimers. Here we maintain our right to draw further disclaimers, if it is necessary for the complete delimitation.
The object of the present inventors was to provide a solution for inhibition of the proliferation or killing of multidrug-resistant cells. Surprisingly it has been found that a group of 8-hydroxyquinoline derivatives are useful for this purpose. The above objectives thus have been solved according to the present invention.